This invention relates to a radio communication apparatus for receiving radio signals at a predetermined period. The radio communication apparatus may be a radio paging receiver, a transceiver, or the like although description will be mainly made in connection with a radio paging receiver.
A radio paging receiver of the type described, receives radio signals when supplied with an electric power from a power source. Each of the radio signals carries a synchronization signal and an additional signal which succeeds the synchronization signal and will become clear as the description proceeds. The radio signals are periodically transmitted by a base station which has a service area within which the paging receiver can receive the radio signals.
The radio paging receiver comprises a power source switch which has an on state and an off state and is connected to the power source. Connected to the power source switch, a first processing circuit processes each of the radio signals into the synchronization and the additional signals when the power source switch is in the on state. It should be understood that the first processing circuit is supplied with the electric power when the switch is in the on state and that the supply of the electric power is associated with the power source switch being in the on state.
Connected to the power source switch, a clock generating circuit generates a timing clock signal when the power source, switch is in the on state. Connected to the power source switch and the first processing and the clock generating circuits, a synchronizing circuit synchronizes the timing clock signal with the synchronization signal as a synchronized clock signal when the power source switch is in the on state.
Connected to the power source switch and the first processing and the synchronizing circuits, a second processing circuit processes the additional signal into a processed signal by using the synchronized clock signal when the power source switch is in the on state. That is, the second processing circuit is capable of dealing with or responding to the additional signal when the paging receiver is put in a synchronized state in which the timing clock signal serves as the synchronized clock signal. Operation of the second processing circuit will be described below in more detail.
When a possessor of the paging receiver turns the power source switch from the off state to the on state, the possessor wishes to know, as soon as possible, whether or not the paging receiver is put in the synchronized state and whether or not the paging receiver is present in the service area. From this viewpoint, it is desirable to make the paging receiver rapidly announce whether or not it is present in the service area immediately after the power source switch is turned from the off state to the on state.